Apparatus for treatment of metal products

ABSTRACT

Apparatus for heat treating and descaling metal without harmful superficial decarburization of the shapes. The apparatus comprises a furnace chamber wherein reducing atmospheres, temperatures between 700* and 1,200* C and vacuums between 100 and 0.01 torr may be maintained. A barometric lock enables steel shapes to be introduced and removed from the furnace chamber without disturbing the vacuum.

United States Patent [191 Gueussier et a1.

APPARATUS FOR TREATMENT OF METAL PRODUCTS Inventors: Andre Gueus sier;Roland Tricot;

Michel Lacoude, all of 73 Albertville, France Assignee: Ugine Aciers,Paris, France Filed: Dec. 16, 1970 Appl. No.: 98,673

Related US. Application Data Continuation-impart of Ser. No. 748,291,July 29, 1968, abandoned.

Foreign Application Priority Data Aug. 1, 1967 France ..67116523 US. Cl...266/4 A, 214/17 13', 214/23 Int. Cl. ..C2ld 1/62 Field of Search..266/4 A, 4 R, 5 R,

May 1, 1973 266/4 E, 4 B; 214/17 B [56] References Cited UNITED STATESPATENTS 1,634,319 7/1927 Callaghan ..266/4 B 3,360,252 12/1967 Westeren266/4 R Primary ExaminerR. Spencer Annear Attorney-Webb, Burden,Robinson & Webb [5 7 ABSTRACT Apparatus for heat treating and descalingmetal without harmful superficial decarburization of the shapes. Theapparatus comprises a furnace chamber wherein reducing atmospheres,temperatures between 700 and 1,200 C and vacuums between 100 and 0.01torr may be maintained. A barometric lock enables steel shapes to beintroduced and removed from the furnace chamber without disturbing thevacuum.

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' INVENTORS ANDRE GUEUSSIER ROLAND TRICOI- MICHEL LACOUDE' wmwm wwiwwAPPARATUS FOR TREATMENT OF METAL PRODUCTS RELATED APPLICATION This is acontinuation-in-part of application Ser. No. 748,291, filed July 29,1968, entitled Process and Apparatus for- Treatment of Metal Productswhich claimed priority under 35 U.S.C. paragraph 119 to French Pat.application No. PV 116,523, filed Aug. 1, 1967. Application Ser. No.748,291 has now been abandoned in favor of continuation application Ser.No. 132,593, filed Apr. 8, 1971.

In the metallurgical industry, products formed by the conventional hotshaping processes such as forging, rolling or stamping have an oxidizedsurface referred to as scale and a structure, particularly hardness,which makes them unsuitable for subsequent cold deforma tion and shapingoperations. In order to continue operations in the cold state, it isnecessary as a rule to perform an annealing heat treatment followed by ascouring operation to eliminate the surface oxides.

In one commercial process currently used, the shapes are heatedelectrically or with liquid or gaseous fuels and mostfrequently inoxidizing atmospheres. Thereafter, the surface oxides are removed in atwostage operation. In the first stage, the shapes are mechanicallyscoured by sanding or shot-blasting, or the shapes are chemicallyscoured or pickled by immersing them in baths of molten salts. In thesecond stage, the shapes are scoured or pickled in an acid bath.According to another process, the shapes are heat treated, for examplein a bath of molten salts, followed by acid stripping or pickling. Inyet another process, the heat treatment is under vacuum followed by acidstripping or pickling.

The industrial methods which consist of heating in a nonoxidizingatmosphere have the important advantage of not causing additionaloxidation on the metal surface. This is also the case when the annealingor tempering treatment is under vacuum as described in the French Pat.No. 1,205,079 of Nov. 3, 1958. According to the teachings of thatpatent, the oxidized steel shapes are heated in a vacuum at atemperature of approximately l,0OO to 1,100 C. Thereafter, the shapesare cooled in the presence of a protective gas. The rate of cooling ofthe shapes in the gas excludes any possibility of fast quenching. in thecase of austenitic stainless steels, the process comprises the steps offirst heating oxidized shapes in a closed container kept under vacuumclose to 0.1 torr at a temperature of approximately l,050 C for severalhours, passing a protective nitrogen atmosphere into the container,transferring the shapes exposed to the atmosphere to a quenching bath,and finally pickling the shapes in an acid bath to eliminate the porouslayer of residual oxide. This process is burdensome and costly. Itcauses superficial decarburization of the steel shapes treated. Finally,this process does not avoid the necessity ofsubsequent scouring orpickling.

In our copcnding application referred to above we described a processfor heat treatment and descaling of metals or of oxidized metal shapeswithout causing harmful superficial decarburization. Shapes treatedaccording to that invention usually do not require subsequent acidpickling to remove the scale.

According to our invention described in our copending application, theoxidized shapes are placed in an enclosure containing a reducingatmosphere under a pressure between and 0.01 torr, and heated totemperatures between 700 and 1,200 C, in contact with a carbonaceousreducing agent, after which they are cooled in a nonoxidizingenvironment.

The carbonaceous reducing agent may be gaseous and may also provide therequired reducing atmosphere. It may also consist of a thin liquid orsolid layer, for example of a hydrocarbon or of a fine suspension of asolid reducing agent, such as graphite in a liquid deposited on thetreated metal. The total quantity of specific carbonaceous reducingagent should be sufficient in each case for all the surface oxides ofthe metal to be reduced, without exerting an action on the metal itself.

The reducing atmosphere may be generated by injection of a gaseousreducing agent into the enclosure. It may also be generated by injectionof a liquid or solid reducing agent, at least partially gasified underthe temperature and pressure conditions prevailing in the enclosure. lnparticular, it may be generated by partial gasification of a thin layerof liquid hydrocarbons deposited on the shapes to be processed.

In this application we describe and claim an apparatus for the practiceof the process described above.

Briefly, according to this invention, a heat treatment furnace isprovided, which essentially comprises a sealed enclosure with pumpingdevices and heating devices, whereby the required pressure andtemperature may be reached and maintained; devices for communicationbetween the surroundings and the enclosure allowing the insertion andwithdrawal of the shapes to be descaled without reducing the vacuum andwithout permitting air to enter the enclosure; means of injection and/orcoating the shapes with a carbonaceous reducing agent; and means forcooling the products in a neutral atmosphere before emerging into theatmosphere.

According to a preferred embodiment, the furnace is isolated from thesurrounding atmosphere by means of at least one barometric lock. Abarometric lock may be fomied in a U-shaped well or elbow filled withthe carbonaceous reducing liquid. One of the branches of the bend is incommunication with the furnace. The other is connected to thesurrounding atmosphere.

The two branches of the bend or well are equipped with lowering andlifting mechanisms which render it possible to insert the shapes to beprocessed through the liquid in the well. It is plain that the outlet ofthe furnace may be equipped with another U-shaped well filled with anyappropriate liquid.

This combination of equipment provides the following results andadvantages: the shapes processed according to our invention are insertedinto the furnace and removed from this furnace without breaking thevacuum seal. They are coated with the carbonaceous reducing agent at thesame time. The nature of the liquid present in the well or wells doesnot affect the atmosphere of the furnace. The components subjected tothe treatment according to our invention may be quenched during theirextraction from the furnace, in a liquid, without being in contact withair.

Further features and other objects and advantages of this invention willbecome clear from the following detailed description made with referenceto the. drawings in which: I

FIG. 1 is a schematic section view of a furnace according to thisinvention;

FIG. 2 is a detailed section through a barometric charging anddischarging joint useful in this invention;

FIG. 3 is a plan view of the elevator system in one of the legs of thebarometric joint; and,

FIG. 4 is a plan view of the elevator mechanism of both legs of thejoint.

One embodiment of this invention, diagrammatically illustrated in asection in FIG. 1-, consists of providing the processing furnace 1 witha toroidal shape having one orifice 2 in communication with a barometricwell or lock 3. The lock 3 is in the shape of a U whose two branches aremarked 4 and 5. The lock simultaneously serves for inserting the shapes(incorporated coating) and of extracting them (with quenching). Itcontains an oil, for example, a quenching oil. In operation, the levelsof oil 6 in the two branches 4 and have the positions shown. The shapesunder treatment travel in a definite direction in the furnace. Theraising and lowering mechanisms (shown schematically as a movablehydraulic piston and cylinder 19, but which could be any other suitableraising and lowering device) take the shape to be treated, 7, lower itto 8 at the bottom of branch 4 below the separation level 9, cause it topass to 10 at the bottom of branch 5 and raise it to 11 up to theorifice 2. The product enters the furnace at 12 and is carried in adefinite direction around the toroidalshaped furnace. A shape which hasalready passed through the furnace is then placed on the raising andlowering mechanisms. The shape is subjected to quenching in the oil ofthe well before moving out into the atmosphere. A continuously operatingfurnace is thus obtained, the vacuum pipe being marked 14 and ahydrocarbon injector 13. The injection of the carbonaceous reducingagent occurs through one or more adjustable valves or through any otheranalogous device. The number and location of such devices corresponds tothe thermal cycle selected, to the desirable vacuum, and to the capacityof the furnace. The heating system is comprised of graphite elements 20,for example.

According to an alternate mode of practicing our invention, the outletof furnace l is a cooling lock 15 having doors l6 and 17. Means 18 areprovided to maintain the atmosphere in the cooling lock inert. I

The joint of FIG. 2 is a U-shaped shaft made up of two cylindricalsleeves connected with one another at the base. Leg of the U isconnected to the furnace interior 26 in a tight manner. The other leg27, which opens into the open air, is sufficiently set off to allowready access to the articles that are to be put into the furnace or tothe articles that have been removed from the furnace. This U-shapedshaft is partially filled with a liquid whose level is established ineach sleeve as a function of the pressure existing above each freesurface. This means particularly that the level of the liquid can be thesame in the two legs when the lock chamber is at atmospheric pressure.This may. be the case when the furnace chamber is under atmosphericpressure. This liquid which is suitable for coating the products thatare to be treated according to the method of the invention (and possiblyfor tempering) fulfills the function of the hydraulic joint, therebyassuring isolation of the lock chamber from the atmosphere.

For the purpose of being introduced into the furnace, the articles thatare to be treated are brought at 28 by means of any fixed or autonomousdevice to the charging elevator (shown in broken lines in the raisedposition at 29) and the elevator is then made to descend to the bottomposition.

This elevator is composed of a frame 31 (FIG. 3) equipped with two setsof guide rollers such as 32 and 33 (FIGS. 2 and 3) which roll onvertical rails such as 34 (FIGS. 2 and 3) in such a manner that thevertical movement will be strictly rectilinear. This frame is coupled toat least one endless chain 35 (FIG.-2) which is guided over its entireelevation and is wound, on the one hand, over a control wheel 36 (FIGS.2 and 4) moved by a set of motor reducers 37 (FIG. 4), and on the otherhand, over a slidably mounted wheel 38 (FIG. 2) for regulating thetension of the chain. Each chain executes a back and forth(ascending-descending) motion whose extreme positions are governed bytwo endof-the-stroke devices, the one for travel at low speed beforestopping, the other for stopping.

When this elevator has been brought to the bottom position 30 (FIG. 2)the immersed charge is pushed by gliding on rails 40 (FIG. 2) toward theelevator 39 (FIGS. 2 and 4) of the lock chamber in its low position. Thedevice used here for pushing the charge is a rack bar pusher 41 (FIG. 4)having a pusher 42 (FIGS. 2 and 4) provided in front with a suitablyshaped shield and on its lower portion with a rack bar having a controlpinion whose movement is assured by a set of motor reducers 43 (FIG. 4)outside of the chamber through a tight rotary joint 44 (FIG. 4). Thepositions of end-ofstroke and stop-on-return are controlled by anend-ofstroke selector likewise positioned outside of the chamber andactuated by the entry shaft of the rotary joint.

When the charge is on the lock chamber side of the leg of the shaft,with a construction similar to the atmosphere side of the leg, it ishoisted to the lock chamber and returned by the transfer device and thenby the furnace charging pusher.

The discharging procedure for the treated product is quite similar. Thetravel from the elevator platform on the lock chamber side of the shaftto the elevator platform on the atmosphere side is assured by anotherrack bar pusher 45 (FIGS. 2 and 4).,

In order to facilitate maintenance and repair, the shaft has a tightcover 46 (FIG. 2) on its upper portion which permits access. It also hasa sliding trap door 47 (FIG. 2) which makes it possible to isolate thefurnace chamber and to reach the corresponding elevator without beingobliged to rupture the vacuum or to change the atmosphere of the lockchamber. This trap door, generally concealed in a protuberance, iscontrolled by an external set of motor reducers which act upon a rackbar hinged to the trap door. The upper portion of the trap door has ajoint which cooperates with a mechanical bearing surface, the closingbeing assured by jacks.

Finally, the lock chamber includes devices for feeding the liquid, forcontrolling the level, for cooling, and recirculating the liquid 50.

In the foregoing, the entry and discharge of the products are madethrough the same shaft. It is also possible to provide a shaftspecialized in one operation at each extremity of the lock chamber. Thensimultaneous maneuvers may be carried out in both shafts which may,moreover, be filled with different liquids.

Having thus described the invention with the detail and particularity asrequired by'the Patent Laws, what is desired protected by Letters Patentis set forth in the following claims.

We claim:

1. A furnace for heat treating and descaling metal shapes consisting ofa wall forming a sealed furnace enclosure, means for maintaining asubatmospheric pressure within said furnace enclosure, means for heatingthe shapes within the furnace enclosure, means for maintaining areducing atmosphere within the furnace enclosure, and means forinserting and extracting the shapes in said enclosure, said insertingand extruding means comprising a U-shaped tube having two upright legscontaining a carbonaceous reducing liquid for coating the shapes priorto entry into the sealed furnace enclosure and for forming a barometriclock therewith, one of said upright legs connected directly to andhermetically sealing with said enclosure, said liquid established atdifferent heights in the different legs of the tube means afterapplication of subatmospheric pressures to the enclosure, means formoving the shapes through the tube means so as to coat the shapes withsaid carbonaceous reducing liquid and then move them into the enclosure.

2. A furnace according to claim 1 in which the extracting meanscomprises a cooling lock and means for maintaining the atmosphere withinthe cooling lock in- 811.

3. A furnace according to claim 1 in which the wall means is toroidal inshape.

4. A device for moving shapes to and from an enclosure maintained atsubatmospheric pressures comprising a U-shaped tube having spacedupright legs, one leg connected directly to and hermetically sealingwith the enclosure and the other communicating with the atmosphere, acarbonaceous reducing liquid in said tube for coating the shapes priorto entry into the sealed furnace enclosure and for forming a barometriclock therewith, said legs sufficiently long to support a barometriccolumn of said fluid, means for raising and lowering the shapes in eachleg so as to coat the shapes with said carbonaceous reducing liquid,means for transferring the shapes from one elevating means to another.

5. A device according to claim 4 in which there is provided a means forpumping fluid from the bottom of the U-shaped tube to the top of the legin communication with the enclosure.

1. A furnace for heat treating and descaling metal shapes consisting ofa wall forming a sealed furnace enclosure, means for maintaining asubatmospheric pressure within said furnace enclosure, means for heatingthe shapes within the furnace enclosure, means for maintaining areducing atmosphere within the furnace enclosure, and means forinserting and extracting the shapes in said enclosure, said insertingand extruding means comprising a U-shaped tube having two upright legscontaining a carbonaceous reducing liquid for coating the shapes priorto entry into the sealed furnace enclosure and for forming a barometriclock therewith, one of said upright legs connected directly to andhermetically sealing with said enclosure, said liquid established atdifferent heights in the different legs of the tube means afterapplication of subatmospheric pressures to the enclosure, means formoving the shapes through the tube means so as to coat the shapes withsaid carbonaceous reducing liquid and then move them into the enclosure.2. A furnace according to claim 1 in which the extracting meanscomprises a cooling lock and means for maintaining the atmosphere withinthe cooling lock inert.
 3. A furnace according to claim 1 in which thewall means is toroidal in shape.
 4. A device for moving shapes to andfrom an enclosure maintained at subatmospheric pressures comprising aU-shaped tube having spaced upright legs, one leg connected directly toand hermetically sealing with the enclosure and the other communicatingwith the atmosphere, a carbonaceous reducing liquid in said tube forcoating the shapes prior to entry into the sealed furnace enclosure andfor forming a barometric lock therewith, said legs sufficiently long tosupport a barometric column of said fluid, means for raising andlowering the shapes in each leg so as to coat the shapes with saidcarbonaceous reducing liquid, means for transferring the shapes from oneelevating means to another.
 5. A device according to claim 4 in whichthere is provided a means for pumping fluid from the bottom of theU-shaped tube to the top of the leg in communication with the enclosure.